1. Field of the Invention
The present invention broadly relates to a battery charging control apparatus and, more particularly, to a charging control apparatus suitable for use in the control of charging of, for example, a battery pack containing a secondary battery which does not exhibit voltage drop generally referred to as -.DELTA.V.
2. Description of the Related Art
In general, there are two types of secondary battery: namely, non-aqueous batteries represented by lithium ion battery and aqueous batteries such as NiCd batteries, NiMH batteries and lead batteries. Unlike aqueous batteries, non-aqueous batteries do not exhibit any inflection point of the battery voltage at the end of the charging. For this reason, different charging methods are used for non-aqueous and aqueous batteries.
More specifically, charging of non-aqueous batteries is conducted by monitoring charging current while maintaining charging voltage constant and terminating the supply of the charging current when the current has become sufficiently small. A typical example of this charging method is "constant-current constant-voltage" method used for lithium ion batteries. In contrast, charging of aqueous batteries terminates when the above-mentioned inflection point is detected. A charging method known as the -.DELTA.V method, used for NiCd batteries and NiMH batteries, is a typical example of such charging methods used for aqueous batteries.
Non-aqueous batteries do not have electrochemical self-protecting function which is exhibited by aqueous batteries. In general, therefore, battery packs incorporating non-aqueous batteries are provided with electric circuits for protection against overcharging. A typical overcharge protection circuit is composed mainly of a detection block which detects the battery voltage and a switching block which performs switching between on and off states of the charging current in relation to the battery voltage. The switching block has a switching element. In a known charging system, the switching block is connected in series to the battery so that it can open the charging current circuit to cut-off the charging current as required. In another known charging system, the switching element is connected in parallel to the batteries so as to selectively bypass the charging current to perform a control of the charging current including turning on and off of the same, thereby controlling the battery voltage to a set level.
As will be seen from the foregoing description, non-aqueous batteries and aqueous batteries employ different types of charging method and, hence, different type of chargers or system. It will be convenient if an aqueous battery charger usable also for non-aqueous batteries is available.
However, since aqueous battery chargers are designed to terminate the charging upon detection of -.DELTA.V, it has been impossible to safely and satisfactorily charge non-aqueous batteries by using this type of charger.